Maximum safe load indicators for cranes



Oct. 3, 1967 J. H. BOUGHTON ,34

MAXIMUM SAFE LOAD INDICATORS FOR CRANES Filed Jan. 18, 1966 M United States Patent M 3,344,934 MAXIMUM SAFE LOAD INDICATORS FOR CRANES John H. Boughton, Amersham Common, England, as-

signor to T. T. Bougliton & Sons Limited, Amersham, England, a British company Filed Jan. 18, 1966, Ser. No. 521,340 3 Claims. (Cl. 212-55) ABSTRACT OF THE DISCLOSURE A slew jib crane has its jib carried by a pedestal structure which is angularly displaceable about a horizontal axis on a base mounted for slewing movement, a bolt extending from the pedestal structure, at a distance from such axis, through an abutment plate fixed to the base and carrying dished resilient discs interposed between the plate and a shoulder on the bolt so as to be deformed upon angular displacement of the pedestal by an upsetting couple, and a switch actuated upon relative movement of the bolt and plate in response to predetermined deformation of the discs, for example, for indicating dangerous loading of the crane.

This invention relates to cranes, and has for its object to provide a construction of crane embodying improved means for indicating when the load being lifted by the crane is approaching, has reached or is in excess of the maximum safe load.

It is well known that the safe load for any particular crane varies with the radius at which the load is being raised. Thus, in the case of a crane with a derricking jib, loads which are safe when the jib is near the vertical Will become increasingly dangerous as the jib is moved towards a horizontal position. Similarly, in the case of a tower crane with a travelling hoist, loads which are safe when the hoist is near the vertical axis of the tower be? come dangerous when the hoist is spaced therefrom.

In the past it has been normal practice, when a safe load indicator has been required on a jib crane, to operate the indicator by measuring the tension in either the hoist rope or the derricking rope. The measurement given in this case is a measurement of the load being lifted and this measurement has to be compensated in accordance with the radius at which the load is being lifted before it can be used to operate a safe load indicator. Such compensation has normally been performed by means of a cam arrangement for which the cam has to be cut specially for each individual crane. This system is therefore expensive and it suffers from a number of disadvantages. Firstly, in the case of a derricking jib crane, the cam must be changed if the length of the jib is altered. Secondly, if the tension measuring device is located in the derrick rope, the cam must be changed if the mechanical advantage of the derricking system is altered. Thirdly, in the case of a crane provided with counterbalance weights, the cam must be changed if the position or number of the weights is changed.

According to the invention, there is provided a slew jib crane (by which is meant a crane having a jib which is mounted for rotational movement in the crane about a vertical axis) comprising a lower base; an upper base mounted thereon for slewing movement relative thereto about a vertical axis; a pedestal structure mounting the jib and hoisting mechanism of the crane, said pedestal structure being in turn pivotally mounted on the upper base so as to possess freedom for limited rotational movement relative thereto about a horizontal axis perpendicular to the longitudinal axis of the jib whenever the upsetting couple acting on the crane reaches a predetermined value Patented Oct. 3, 1967 representing a condition of loading of the crane approaching, coinciding with orexceeding the maximum safe loading condition for which the crane has been designed; con- .trol means operative in response to the occurrence of said rotational movement; and means operable under the control of said control means to give a warning signal to the operator of the crane of the existence of said condition of loading and/ or to stop or initiate stoppage of the hoisting gear of the crane.

In the case of a derricking jib crane the horizontal axis aforesaid is preferably located on the same side of the pivotal mounting of the jib as the load.

It is to be understood that the term jib, unless otherwise indicated, includes both a derricking jib and also a horizontal non-derricking jib, for example of a tower crane, along which a load carriage travels in the operation of the crane.

The crane of this invention may be a mobile crane in which the crane proper is mounted on a caterpillar or endless tracked chassis or on a wheeled chassis.

Such mobile crane may be a tractor-mounted crane or a tractor-drawn crane.

In the former case the construction may be one in which, as in the particular embodiment of the invention hereinafter described, the jib and hoisting mechanism of the crane are mounted through the intermediary of a pedestal structure on an arch-like support for these parts over-spanning the tractor frame and rigidly afiixed thereto.

The invention will now be further described with reference to the accompanying drawings, which illustrate the aforesaid particular embodiment of the invention by way of example, the crane in this embodiment being a derricking jib tractor-mounted crane.

In these drawings:

FIGURE 1 is an elevational view of the crane, the view being largely diagrammatic;

FIGURE 2 is a fragmentary elevational view of the crane showing on a larger scale than FIGURE -1 the manner of mounting the pedestal structure aforesaid, on which the jib and hoisting mechanism of the crane are mounted, on the arch-like support, also aforesaid, of the crane structure; and

FIGURE 3 is a fragmentary vertical section, drawn on a larger scale than'FIGURE 2, illustrating the control means aforesaid of the crane.

Like reference numerals indicate like parts in the various figures.

The crane shown comprises a tractor unit 1 mounting an arch 2 over-spanning the tractor framework and rigidly afiixed thereto.

Arch 2 mounts a pedestal structure 3 through the intermediary of a turntable comprising an upper member 4 and a lower member 5.

Lower member 5 is fast with arch 2 and upper member 4 is revolubly mounted on lower member 5 so as to be rotatable about a fixed vertical axis located at the centre of the arch 2 on the longitudinal centre line of the crane.

Normally, pedestal structure 3 would be in fixed relation to upper turntable member 4. In the crane of this invention, however, it is pivotally mounted thereon, through a pivot 6, so as to possess freedom for rotational movement about the axis of pivot 6 and therefor about an axis perpendicular to the longitudinal axis of the crane jib, which latter is marked 7, is pivoted to pedestal structure 3 at 8 and is raised and lowered about its pivot by an hydraulically operated derricking mechanism 9, according to conventional practice.

Upstanding from the upper turntable member 4 is an abutment plate 10 and incorporated with pedestal structure 3 is a lug 11 mounting an approximately horizontally disposed bolt 12 formed with a circular disc-shaped head 13 and with a shank portion 14 extending therefrom through a hole provided to receive it, with a sliding fit, in abutment plate 10, said shank portion having at the outer end thereof a screw threaded portion on which a nut 16 is threaded.

Interposed between head 13 of bolt 12 and abutment plate 10 are a pair of stifily resilient metal discs 17, 18 of dished formation threaded over shank portion 14 of bolt 12 edge to edge and with the dished sides of the respective discs directed towards one another.

The arrangement is such that normally, i.e., prior to the upsetting couple acting on the crane as the latter is lifted a load reaching the predetermined value aforesaid, i.e., the value representing a condition of loading of the crane approaching, coinciding with or exceeding the maximum safe loading condition, there is no freedom for movement of the assembly comprising the pedestal structure 3 and the parts mounted thereon about pivot 6; the intervention of discs 17, 18 between head 13 of bolt 12 and abutment plate 10 prevents such movement. As soon, however, as the upsetting couple commences to exceed said predetermined value discs 17, 18 commence to yield compressively with the resulting actuation of a microswitch '19 controlling the circuit (not shown) of an electrically operated signal device operative to give to the operator of the crane a warning to the effect that the crane is being overloaded or is operating near to this condition.

The signal device may take any desired form. It may be designed to give an audible signal or a visual one, or both, and alternatively to the use of a signal device, or additionally thereto, a device, brought into operation by the microswitch 19 (which in this embodiment of the invention constitutes the control means aforesaid), may be used, as already indicated, effective to stop, or initiate stoppage, of the hoisting mechanism of the crane.

If desired, the arrangement may be one in which the signal means gives a plurality of successive signals corresponding respectively to successively increasing conditions of loading of the crane. For this purpose, two or more microswitches may be used, operable in succession as discs 17, 18 compress to progressively further extent under progressively increasing values of the upsetting couple acting on the crane.

In the case of application of the invention to a tower crane as hereinbefore referred to it is preferable to pivot the jib carrying the travelling hoist to the vertical structure forming the tower of the crane, arranging the control means in the joint between the jib and said vertical structure.

Various modifications are possible. For example, elements acting tensionally may be employed in place of the compressively acting discs 17, 18. In this case said elements may be located above the rear of arch 2 of the crane structure instead of above the front thereof as in the construction illustrated. Also, the signal means or as the case may be, the means for stopping or initiating stoppage of the hoisting gear may be pneumatically or bydraulically operated instead of being electrically operated. All such modifications are to be understood as within the scope of the invention.

Finally, it will be understood that in the particular embodiment of the invention described above and illustrated in the drawings, upper turntable member 4 constitutes the upper base hereinbefore referred to and the unit comprising lower turntable member 5 and arch 2 the lower base.

What I claim as my invention and desire to secure by Letters Patent of the United States is:

1. A slew jib crane comprising a lower base, an upper base mounted on said lower base for slewing movement relative thereto about a vertical axis, a pedestal structure pivotally mounted on said upper base for limited angular displacement relative thereto about a first horizontal axis, a jib pivotally mounted on said pedestal structure for derricking movement about an axis parallel to said first horizontal axis, a bolt attached to said pedestal structure and being spaced substantially from said first horizontal axis, an abutment forming member fixed to said upper base and having an opening through which said bolt extends, means defining a shoulder on said bolt which is movable toward said abutment upon angular displacement of said pedestal structure about said first horizontal axis by an upsetting couple resulting from loading of the crane, a pair of resilient discs mounted on said bolt between said abutment and said shoulder to yieldably resist angular displacement of the pedestal structure by said upsetting couple, and switch means responsive to deformation of said resilient discs by an upsetting couple exceeding a predetermined value.

2. A slew jib crane according to claim 1, wherein said discs are of dished formation and abut one another at their edges with their dished sides facing each other.

3. A slew jib crane according to claim 1, wherein switch means is mounted on said abutment forming member and is engageable by said bolt so as to be actuated by movement of said bolt relative to said abutment in response to said deformation of the discs.

References Cited UNITED STATES PATENTS 1,614,575 1/1927 Siebs 212-39 2,910,189 10/1959 Scheuernelug 2l239 3,223,249 12/1965 Cady 21239 3,278,925 10/1966 Saunders et al 212-39 3,282,441 1/1966 Staotfer 212-35 ANDRES H. NIELSEN, Primary Examiner. 

1. A SLEW JIB CRANE COMPRISING A LOWER BASE, AN UPPER BASE MOUNTED ON SAID LOWER BASE FOR SLEWING MOVEMENT RELATIVE THERETO ABOUT A VERTICAL AXIS, A PEDESTAL STRUCTURE PIVOTALLY MOUNTED ON SAID UPPER BASE FOR LIMITED ANGULAR DISPLACEMENT RELATIVE THERETO ABOUT A FIRST HORIZONTAL AXIS, A JIB PIVOTALLY MOUNTED ON SAID PEDESAL STRUCTURE FOR DERRICKING MOVEMENT ABOUT AN AXIS PARALLEL TO SAID FIRST HORIZONTAL AXIS, A BOLT ATTACHED TO SAID PEDESTAL STRUCTURE AND BEING SPACED SUBSTANTIALLY FROM SAID FIRST HORIZONTAL AXIS, AN ABUTMENT FORMING MEMBER FIXED TO SAID UPPER BASE AND HAVING AN OPENING THROUGH WHICH SAID BOLT EXTENDS, MEANS DEFINING A SHOULDER OR SAID BOLT WHICH IS MOVABLE TOWARD SAID ABUTMENT UPON ANGULAR DISPLACEMENT OF SAID PEDESTAL STRUCTURE ABOUT SAID HORIZONTAL AXIS BY AN UPSETTING COUPLE RESULTING FROM LOADING OF THE CRANE, A PAIR OF RESILIENT DISCS MOUNTED ON SAID BOLT BETWEEN SAID ABUTMENT AND SAID SHOULDER TO YIELDABLY RESIST ANGULAR DISPLACEMENT OF THE PEDESTAL STRUCTURE BY SAID UPSETTING COUPLE, AND SWITCH MEANS RESPONSIVE TO DEFORMATION OF SAID RESILIENT DISCS BY AN UPSETTING COUPLE EXCEEDING A PREDETERMINED VALUE. 